I looked all over the archives and couldn't find anything on this so here goes: My brake failure light had been coming on, and I noted that the front calipers would sometimes lock up a bit on full lock parking maneuvers. I reasoned the front flex hoses needed replacing. After replacing all four flex hoses, doing a fluid change and bleeding the system, the lock up issue was solved and the light went off. I thought all was well until, after a few drives, the warning light started coming on again. First intermittently, now all the time. I suspect that the piston seal on one side of the shuttle in the pressure switch may be compromised, causing just enough pressure differential to gradually push the shuttle over and activate the switch. Has anyone pulled one of these units apart and done a rebuild? Looks like a fiddly job. The brakes are fine and I could just disconnect the switch wire for now, but I'd rather fix it correctly over the winter.
The pressure switch on the pressure differential warning block tend to fail. you can unscrew the switch without introducing air into the brake system and test it. The switches fail, causing the light to come on. You can get a new switch from Porsche. early 911's use the same part. You can take the block apart and clean up all of the seals and piston, but I have never seen replacement seals for the block.
I took the dif pressure switch apart on my 308. Cleaned out the pistons and the switch itself from old dirt and rust and lubricated everything. It has been working well ever since (Or better worded; it has not indicated any brake failures since then). Best Peter
The part number for the switch is Bosch 0-343-102-010. It it a single terminal switch that grounds through the body of the unit. They are used on early Porsches: http://www.pelicanparts.com/More_Info/0343102010.htm?pn=0-343-102-010-INT&gclid=CjwKCAiAo9_QBRACEiwASknDwXlQWoT87zBMuFZ6nLaGS91bHZVV-JXRHSk-_4R3tIFKKizpvdsxuxoCECQQAvD_BwE Make sure that the supplier is selling you a single terminal switch as they used switches with two terminals as well
Daryl, See pics attached for guts of unit. I tried to find new seals as well with no luck. The original ones are not too bad so I will reuse them and hope they work. Pretty simple concept. Image Unavailable, Please Login
